Knit hat

A knit winter hat that covers your ears will keep
you warm in cold temperatures and windy conditions.
Alternatively, a hoodie can keep your head and neck
warm, but isn't always great at keeping your ears warm.

Sunglasses

Sunglasses will keep the sun out of your eyes
and protect them from its harmful rays.
They can also help keep wind or precipitation out of your eyes.
The best sunglasses will be lightweight and have ample UV protection.
Interchangable lenses will give you the most flexibility.

Long-sleeved shirt

When the weather is cooler a long-sleeved shirt is ideal.
Technical fabrics are a must for keeping the sweat off your skin.

Light jacket

A light jacket over a long-sleeved shirt on cold days
will keep you just warm enough. Your best option will be something
wind and waterproof, as well.

Tights

Tights or long pants will keep your legs warm when
the temperature drops, and the right fabric can provide good
sheilding from the wind and rain. When it's extremely cold,
a combination of pants over top of tights will give you the most
warmth and still keep you comfortable.

Lightweight gloves

A pair of thin gloves will provide just enough warmth for cool temps.
Those made with technical fabrics are best, and will do a good job of
wicking away sweat. They'll also be easy to stash in a pocket if they
end up not being needed.

Sunblock

Prevent sunburn and exposure to harmful
UV rays by getting some sunblock -- ideally one
with a 30 SPF rating or higher.

Identification

It's always a good idea to be prepared for
possible trouble. Keep some ID on you in case the worst
happens. Throw your license or business card in your back
pocket, or better yet -- use something like a
RoadID that can also
contain additional vital information if you're in trouble.